This invention relates to a process for the production of tertiary butanol from isobutene. More particularly, the invention relates to a fixed bed catalytic process.
The acid catalysis of the reaction of isobutene and water to produce t-butanol is well known. More recently, acid ion exchange resins have been used as the catalysts, e.g., British Patent Specifications 1,390,164 and 1,396,488, where the reaction of propylene and water was illustrated in a fixed bed acidic ion exchange resin.
Commercial operations would have to be continuous to be feasible. Fixed bed procedures were initially proposed as the most desirable because of simplicity of operation, i.e., water and isobutene are passed over the catalyst, the phases separated and t-butanol separated from the organic phase and/or the water phase. The reaction is exothermic and temperature control has presented a problem. Temperature control may be effected by increasing the amount of water in the reaction. However, another problem which is a serious detriment is a rapid increase in by-product formation. At the beginning of the process, the reaction proceeds as expected, with high selectivity for the production of t-butanol. Side reactions begin and increase as the reaction proceeds, with a substantial reduction of t-butanol formation. The side reactions include particularly polymerization, which is uncontrolled and from which results diisobutene, triisobutene, higher oligomers, and codimers of isobutene and n-butenes.
The formation of diisobutene and triisobutene may not be particularly undesirable since these materials are of commercial interest. The higher oligomers, however, are substantially waste and in some cases, are dark, gummy materials, which can foul equipment or otherwise interfere with the process. Furthermore, the uncontrolled side reaction is a detriment, since product distribution cannot be adjusted as desired. It should also be noted in the prior art that by-product selectivity could be reversed only by the cessation of the reaction, back-washing of the catalyst with water or replacement of the catalyst.
U.S. Pat. No. 3,328,471, issued to Kronig et al, appreciated these problems in the fixed bed system, and determined that the problems as described in the fixed bed were not soluble and abandoned the fixed bed for a fluidized system. The Kronig et al process consists of isobutene, water and finely granular cation exchange resin, which are vigorously mixed in a reactor(s), separated into hydrocarbon phase and a water phase, which contains the resin catalyst. t-Butanol is recovered by distillation from the hydrocarbon phase, and the waterresin phase is recycled to the reactor. Catalyst and water, which are lost, are made up in order to maintain the desired ratios. This system is cooled at a number of points, thus making temperature control easy. The selectivity to t-butanol remained high. Because the Kronig et al system depends on emulsification of the three-component system to obtain reaction, the use of an emulsifier is suggested.
The fluidized system of Kronig et al is inherently less desirable because the catalyst is mixed into the reactants and some portion may remain in the hydrocarbon fraction, requiring an additional separation, whereas the fixed bed does not, i.e., the catalyst will generally remain in the aqueous phase. However, the agitation of the fluidized system results in disintegration of some catalysts and the fines are likely to be dispersed in both the aqueous and hydrocarbon phases.
The disintegration of the catalysts in the fluidized bed requires freguent makeup to maintain the reaction because the amount of catalyst present in this type of system is generally less than in a fixed bed. Larger amounts of aqueous phase and catalyst may, of course, be employed in the fluidized bed; however, handling problems and energy required to pump excess catalyst through the system are contraindicative of that. It should also be appreciated that larger amounts of catalyst will be lost when larger amounts of the catalyst are employed, although makeup for maintaining the reaction may be less frequent.
The energy requirements of the fluidized system are also greater for any given amount of reactants than the fixed bed, since the pumping of the aqueous slurry and the agitation of the reactants are excessive beyond fixed bed handling.
As noted above, the fluidized system may be improved by the use of emulsifiers. The emulsifiers are contaminants which may require special handling for their removal.
It is an advantage of the present invention that benefits of the fixed bed isobutene hydrations and the fluidized system are both obtained. It is another advantage of the present invention that an improved fixed bed isobutene hydration process for the preparation of t-butanol has been obtained. It is a particular feature of the present invention that a method of suppressing (or controlling) isobutene polymerization in a fixed catalyst bed has been obtained. It is also a feature of the present invention that temperature control of the fixed bed hydration has been obtained. These and other advantages and features will be more apparent from the further discussion of the invention. Another advantage is the elimination of the water phase from the product stream and the resultant corrosion problems therefrom.